Specific helium-neon laser sensitivity of the purified cytochrome c oxidase

Purpose: In order to gain some insight into the mechanism of interaction between Helium-Neon (He-Ne) laser light and mitochondrial cytochromes, the sensitivity of cytochrome electron transfer activity to He-Ne laser was tested. Materials and methods: Irradiation of solutions containing either purified cytochromes or dissolved rat liver mitochondria was carried out (wavelength 632.8 nm, fluence rate 10 mW cm-2, fluence 2 J cm-2); the irradiation conditions were the ones able to affect cytochrome c oxidase (COX) activity in mitochondria. Results: Cytochrome c oxidation catalysed by COX was affected by He-Ne laser irradiation of the purified enzyme. This result was obtained from measurements of the pseudo-first-order kinetic constant and from determinations of the turnover number of the enzyme, performed at different cytochrome c/COX ratios. Consistently, the kinetic parameters of COX changed. On the contrary, no alteration in the rate of electron transfer catalysed by either cytochrome c or bc1 complex was found. Conclusions: This study shows that purified COX is a specific target of He-Ne laser light; therefore, COX may be considered to be a mitochondrial photo-acceptor